Fluoride based composite material and method for making the same

ABSTRACT

A filler material that includes a metal fluoride compound which is coated with silica. The filler material can be used in various types of covering agents.

The present invention is a continuation-in-part of U.S. patentapplication Ser. No. 11/256,839 filed Oct. 24, 2005, which isincorporated herein by reference.

The present invention relates to a fluoride-based material that can beused in a variety of applications such as, but not limited to, paintfillers.

BACKGROUND OF THE INVENTION

Filling materials are typically lower cost components that are used toprovide bulk to various types of components and/or enhance or extendfunction of one or more other components in a product. For example,paints typically include a pigment composition to achieve the desiredcolor and hiding power of the paint. Many interior and exterior paintsinclude hiding white-pigments. Other tints and colors can be mixed withthe white pigments to obtain various colored paints. The pigments usedin the paint can include inorganic and organic pigments, pigment lakes,insoluble dyes and other durable coloring matter. While the pigmentationof the paint can be solely from prime pigments, it is economicallyimpractical to use solely prime pigments at the indicated high pigmentvolume concentration. As such, it is common that the pigment in thepaint includes a hiding prime pigment and a pigment extender. Therelative proportions of the prime white pigment and the pigment extenderin the pigment mixture may be varied widely, but usually the hidingprime pigment is present at a pigment volume concentration whichprovides the desired paint covering power or hiding and the extenderpigment is present in an amount which provides the paint with thedesired total pigment volume concentration.

Common pigment extenders that are used in paints include calciumcarbonate, talc, barytes, magnesium silicates, aluminum silicates,diatomaceous earth, china clay, asbestine, silica and mica. The need forimproved extenders and/or fillers for products continues to exist. Thepresent invention is directed to a material and a method and amanufacturing process for making such material that can be used as afiller in a variety of products and/or as a pigment extender in paints,coatings, stains, varnishes, primer, lacquers, sealants, caulks, etc.

SUMMARY OF THE INVENTION

The present invention is directed to a novel filler material and amethod and process for manufacturing such novel filler material. Thefiller can be used as the sole filler or in combination one or moreother types of fillers. Also, when the filler material is at leastpartially used as a pigment extender, the filler material can be thesole pigment extender or be used in combination with one or more otherpigment extenders. The filler material of the present invention can beused to reduce the amount of crystalline silica that is included in aparticular type of product and/or to reduce the raw material cost of aparticular product. In some applications, the filler material of thepresent invention can enhance one or more properties of a product (e.g.,increasing the hiding power of paint, increased matting of paint,improved scrub touch up and burnish resistance of paint, increase thecontrast ratio of paint, lower the gloss and sheen of the paint, etc.).

In one non-limiting aspect of the present invention, the novel fillermaterial of the present invention is a metal fluoride compound that iscoated with silica (e.g., amorphous silica, etc.). In one non-limitingembodiment of the invention, the metal fluoride compound includescalcium fluoride; however, it can be appreciated that other oradditional metal fluoride compounds can be used. In one non-limitingaspect of this embodiment, a majority weight percent of the metalfluoride compound includes calcium fluoride. In another and/oradditional non-limiting aspect of this embodiment, at least about 70weight percent of the metal fluoride compound includes calcium fluoride.In still another and/or additional non-limiting aspect of thisembodiment, at least about 80 weight percent of the metal fluoridecompound includes calcium fluoride. In yet another and/or additionalnon-limiting aspect-of this embodiment, at least about 90 weight percentof the metal fluoride compound includes calcium fluoride. In still yetanother and/or additional non-limiting aspect of this embodiment, atleast about 99 weight percent of the metal fluoride compound includescalcium fluoride. In another and/or additional non-limiting aspect ofthis embodiment, the metal fluoride compound, when including calciumfluoride, can include calcined and/or non-calcined calcium fluoride. Inanother and/or additional non-limiting embodiment of the invention, themetal fluoride compound content of the filler material is generallyabout 50-99 weight percent of the novel filler material. In onenon-limiting aspect of this embodiment, the metal fluoride compoundcontent of the filler material is generally about 55-90 weight percentof the novel filler material. In still another and/or additionalnon-limiting aspect of this embodiment, the metal fluoride compoundcontent of the filler material is generally about 60-80 weight percentof the novel filler material. In yet another and/or additionalnon-limiting aspect of this embodiment, the metal fluoride compoundcontent of the filler material is generally about 60-75 weight percentof the novel filler material. In still yet another and/or additionalnon-limiting aspect of this embodiment, the metal fluoride compoundcontent of the filler material is generally about 65-75 weight percentof the novel filler material. In yet another and/or additionalnon-limiting embodiment of the invention, the silica content of thecoated metal fluoride is generally about 1-40 weight percent of thenovel filler material. In one non-limiting aspect of this embodiment,the silica content of the filler material is generally about 5-35 weightpercent of the novel filler material. In another and/or additionalnon-limiting aspect of this embodiment, the silica content of the fillermaterial is generally about 10-35 weight percent of the novel fillermaterial. In still another and/or additional non-limiting aspect of thisembodiment, the silica content of the filler material is generally about15-30 weight percent of the novel filler material. In yet another and/oradditional non-limiting aspect of this embodiment, the silica content ofthe filler material is generally about 15-25 weight percent of the novelfiller material. In still yet another and/or additional non-limitingembodiment of the invention, at least about 1 percent of the outersurface of the metal fluoride compound is coated with the siliconcompound. In one non-limiting aspect of this embodiment, at least about10 percent of the outer surface of the metal fluoride compound is coatedwith the silicon compound. In another and/or additional non-limitingaspect of this embodiment, at least about 25 percent of the outersurface of the metal fluoride compound is coated with the siliconcompound. In still another and/or additional non-limiting aspect of thisembodiment, at least about 40 percent of the outer surface of the metalfluoride compound is coated with the silicon compound. In yet anotherand/or additional non-limiting aspect of this embodiment, at least amajority of the outer surface of the metal fluoride compound is coatedwith the silicon compound. In still yet another and/or additionalnon-limiting aspect of this embodiment, at least about 80 percent of theouter surface of the metal fluoride compound is coated with the siliconcompound.

In another and/or alternative non-limiting aspect of the presentinvention, the average particle size of the novel filler material of thepresent invention is generally no greater than about 100 microns. In onenon-limiting aspect of this embodiment, the average particle size of thenovel filler material of the present invention is generally no greaterthan about 80 microns. In another and/or additional non-limiting aspectof this embodiment, the average particle size of the novel fillermaterial of the present invention is generally about 1-60 microns. Instill another and/or additional non-limiting aspect of this embodiment,the average particle size of the novel filler material of the presentinvention is generally about 2-40 microns. In yet another and/oradditional non-limiting aspect of this embodiment, the average particlesize of the novel filler material of the present invention is generallyabout 5-30 microns. In still yet another and/or additional non-limitingaspect of this embodiment, the average particle size of the novel fillermaterial of the present invention is generally about 8-20 microns. Ascan be appreciated, larger or smaller particle sizes can be used.

In yet another and/or alternative non-limiting aspect of the presentinvention, the filler material of the present invention can be formedfrom precipitation from an aqueous solution containing fluorinecontaining acid. In one non-limiting embodiment of the presentinvention, the fluorine containing acid includes hydrofluorosilicicacid; however, other or additional fluorine containing acids can beused. In one non-limiting aspect of this embodiment, at least about 10weight percent of the fluorine-containing acid includeshydrofluorosilicic acid. In another and/or additional non-limitingaspect of this embodiment, at least about 50 weight percent of thefluorine containing acid includes hydrofluorosilicic acid. In stillanother and/or additional non-limiting aspect of this embodiment, atleast about 75 weight percent of the fluorine-containing acid includeshydrofluorosilicic acid. In yet another and/or additional non-limitingaspect of this embodiment, at about 80-100 weight percent of thefluorine-containing acid includes hydrofluorosilicic acid. In anotherand/or additional non-limiting embodiment of the present invention, oneor more other acids can be included with the fluorine-containing acid(e.g., hydrochloric acid, etc.); however, this is not required. In yetanother and/or additional non-limiting embodiment of the presentinvention, the source of fluorine-containing acid can be from a wastestream from another chemical process; however, this is not required. Theconcentration of the fluorine-containing acid varies depending on thesource of the fluorine-containing acid. For instance, if the primarysource of fluorine-containing acid is from a waste stream of anotherchemical process, the concentration of the fluorine-containing acid istypically low. In one non-limiting example, the concentration of thefluorine-containing acid in a waste stream used to form the fillermaterial of the present invention is about 0.05-5% acid. In anothernon-limiting example, the concentration of the fluorine-containing acidin a waste stream used to form the filler material of the presentinvention is about 0.1-2% acid. In still another non-limiting example,the concentration of the fluorine-containing acid in a waste stream usedto form the filler material of the present invention is about 0.2-1%acid. As can be appreciated, the concentration of thefluorine-containing acid can be higher in some waste streams and/or whenthe fluorine-containing acid is from a source other than a waste stream.

In still yet another and/or alternative non-limiting aspect of thepresent invention, the filler material of the present invention can beformed from precipitation from an aqueous solution containingfluorine-containing acid in one or more stages. In one non-limitingembodiment of the invention, at least one reactor tank or vessel is usedto at least partially form the filler material. In one aspect of thisembodiment, the source of aqueous solution containingfluorine-containing acid is fed directly into a reactor tank or vessel.The source of aqueous solution containing fluorine-containing acid thatis fed into the reactor tank or vessel can 1) come directly from a wastestream, 2) come from a storage tank that contains a source offluorine-containing acid, etc. In one non-limiting arrangement, thesource of fluorine-containing acid that is fed into a reactor tank orvessel is at least partially from a storage tank. The storage tank canbe designed to supply a steady or continuous supply of thefluorine-containing acid to the reactor tank or vessel. The storage tankcan be at least partially supplied with fluorine-containing acid from awaste stream that includes fluorine-containing acid and/or can be atleast partially supplied from another source of fluorine-containingacid.

In another and/or alternative non-limiting aspect of the presentinvention, a source of base is added to one or more of the reactor tanksor vessels to be at least partially reacted with the source offluorine-containing acid. In one non-limiting embodiment of theinvention, the source of calcium includes calcium oxide, calciumhydroxide M_(g)O, M_(g)(OH)₂, Na₂O, N_(a)OH, etc. One non-limitingaspect of this embodiment, the base source is lime and/or hydrated lime;however, other or additional bases can be used. In another and/oradditional non-limiting aspect of this embodiment, the source of baseincludes a majority weight percent calcium oxide. In another and/oradditional non-limiting aspect of this embodiment, the source of baseincludes about 80-100 weight percent calcium oxide. In yet anotherand/or additional non-limiting aspect of this embodiment, the source ofbase includes about 80-100 weight percent lime and/or hydrated lime. Inanother and/or additional non-limiting embodiment of the invention, thesource of base has an average particle size of no greater than about 100microns. In one non-limiting aspect of this embodiment, the source ofbase has an average particle size of about 1-60 microns. In anotherand/or additional non-limiting aspect of this embodiment, the source ofbase has an average particle size of about 2-40 microns.

In still another and/or alternative non-limiting aspect of the presentinvention, a sufficient amount of a base is added to one or more of thereactor tanks or vessels to cause the pH in the first reactor tank orvessel to increase. Typically, the pH of the acid stream that includes asource of fluorine-containing acid is less than about 4, and typicallyless than about 3, and more typically about 2 or less. A sufficientamount of a base is added to the source of fluorine-containing acid tocause the pH of the mixture to increase at least about 0.25 pH,typically at least about 0.5 pH, and more typically at least about 1 pH.As can be appreciated, sufficient amounts of abase can be added to thereactor tank or vessel in amounts to increase the pH in the firstreactor tank or vessel by more than 1 pH. In one non-limiting embodimentof the invention, a sufficient amount of a base is added to the finalreactor tank or vessel to cause the pH of the solution in the finalreactor tank or vessel to be increased to at least about 5.5 pH,typically at least about 6 pH, and more typically about 6-8 pH; however,a higher pH can be obtained. As can also be appreciated, other oradditional materials can be added to the one or more reactor tanks orvessels to increase the pH in the one or more reactor tank and vessel. ApH of greater than about 8 generally is generally sufficient to stopfurther reaction of the components to form the filler material in thefinal reactor tank or vessel. When one reactor tank or vessel is used toform the filler material, the pH in the reactor tank is increased overtime until the pH is at least about 5.5-6 pH, and more typically about6-8 pH. When two reactor tanks or vessels are used to form the fillermaterial, the pH in the first reactor vessel is typically increased fromabout 0.5-4 pH to a pH of about 1.5-5, and the pH is then increasedfurther in the second reactor tank or vessel from about 1-4 pH to about6-8 pH. As can be appreciated, other pH increases in the two reactortanks or vessels can be used. When more than two reactor tanks are usedto form the filler material, other pH increases in the reactor tanks orvessels can be used.

In yet another and/or alternative non-limiting aspect of the presentinvention, the source of base and a source of fluorine-containing acidin the reactor tank or vessel can be agitated to promote a reactionbetween the two components; however, this is not required. In onenon-limiting aspect of the invention, the reactor tank or vessel isagitated by continuous or intermediate stirring; however, other oradditional types of agitation can be used.

In still yet another and/or alternative non-limiting aspect of thepresent invention, at least two reactor tanks or vessels are used to atleast partially form the filler material. In one non-limiting embodimentof the invention, the source of aqueous solution containingfluorine-containing acid and a source of base are fed into a firstreactor tank or vessel. In the first reactor tank or vessel, at least aportion of the aqueous solution containing fluorine-containing acid anda source of base react to form the filler material. At least a portionof the formed filler material, at least a portion of the unreactedaqueous solution containing fluorine-containing acid is fed into asecond reactor tank or vessel. As can be appreciated, anyfluorine-containing acid that has not reacted in the first reactor tankor vessel may also be fed into the second reactor tank or vessel. In thesecond reactor tank or vessel, further reaction between the solutioncontaining fluorine-containing acid and a source of base react to formadditional filler material. Additional amounts of a solution containingfluorine-containing acid and/or a source of base can be added to thesecond reactor tank or vessel; however, this is not required. In oneparticular non-limiting arrangement, only a source of base is added tothe second reactor tank or vessel. The materials in the second reactortank or vessel can be agitated; however, this is not required. Inanother and/or additional non-limiting arrangement, overflow from thefirst reactor tank or vessel is fed into the second reactor tank orvessel. In still another or additional non-limiting arrangement, asufficient amount of a base is added to the second reactor tank orvessel to cause the pH in the second reactor tank or vessel to increaseto about 6-8 pH.

In another and/or alternative non-limiting aspect of the presentinvention, a portion of the content in the first reactor tank is fedback to the steady state tank so as to at least partially moderate thepH on the steady state tank. In one non-limiting embodiment of theinvention, 1-50% of the flow of material from the first reactor tank orvessel is added back to the steady state tank. In one aspect of thisembodiment of the invention, 5-25% of the flow of material from thefirst reactor tank or vessel is added back to the steady state tank. Ascan be appreciated, other amounts of material from the first reactortank or vessel can be added back to the steady state tank.

In still another and/or alternative non-limiting aspect of the presentinvention, the material from one or more of the reactor tanks or vesselsis at least partially flocculated with one or more polymers. In onenon-limiting embodiment of the present invention, the one or morepolymers used for flocculation include an organic polymer. Onenon-limiting example of a polymer that can be used is Drewfloc 2270manufactured by Ashland Chemical Company. In another and/or additionalnon-limiting embodiment of the present invention, the one or morepolymers for flocculation are added to the filler material after thefiller material has exited that last reactor tank or vessel. In stillanother and/or alternative non-limiting embodiment of the invention, oneor more polymers for flocculation are added to the product stream fromthe last reactor tank or vessel at a rate of at least about 0.01 weightpercent based on the solid content of the product stream. In onenon-limiting aspect of this embodiment, one or more polymers forflocculation are added to the product stream from the last reactor tankor vessel at a rate of about 0.01-4 weight percent based on the solidcontent of the product stream. In another and/or alternative onenon-limiting aspect of this embodiment, one or more polymers forflocculation are added to the product stream from the last reactor tankor vessel at a rate of about 0.02-1 weight percent based on the solidcontent of the product stream. In still another and/or alternative onenon-limiting aspect of this embodiment, one or more polymers forflocculation are added to the product stream from the last reactor tankor vessel at a rate of about 0.04-0.5 weight percent based on the solidcontent of the product stream. In yet another and/or alternativenon-limiting aspect of this embodiment, one or more polymers forflocculation are added to the product stream from the last reactor tankor vessel at a rate of about 0.05-0.15 weight percent based on the solidcontent of the product stream. As can be appreciated, other amounts ofpolymer for flocculation can be used.

In still another and/or alternative non-limiting aspect of the presentinvention, the filler material from the last reactor tank or vessel isdirected into a slurry thickening vessel to allow the filler material tothicken; however, this is not required. In one non-limiting embodimentof the invention, the solid content of the product stream from the lastreactor tank or vessel for forming the filler material is about 1-8weight percent. The product stream is at least partially directed into aslurry thickening vessel to allow the filler material to settle to thebottom the slurry thickening vessel. The product stream that includesthe filler material can include a flocculating agent; however, this isnot required. The solid content of the filler material that settles ator near the bottom of the slurry thickening tank is at least about 10weight percent solids, typically at least about 15 weight percentsolids, more typically about 15-40 weight percent solids, and even moretypically about 15-20 weight percent solids. The filler material has anaverage surface area of about 30-150 m²/g.

In yet another and/or alternative non-limiting aspect of the presentinvention, the thickened slurry from the slurry thickening vessel can beprocessed to remove oversize particles and/or contaminated particles inthe thickened slurry; however, this is not required. In one embodimentof the invention, the thickened slurry from the slurry thickening vesselis at least partially subjected to a hydrocyclone. As can beappreciated, other or additional process can be used to remove liquids,oversize particles and/or contaminated particles in the thickenedslurry.

In still yet another and/or alternative non-limiting aspect of thepresent invention, liquid is removed from the slurry so as to form adrier filler material. In one non-limiting embodiment of the invention,a filter such as, but not limited to, a drum filter, cyclonic filter orthe like can be used to remove liquid from the slurry. In another and/oralternative non-limiting embodiment of the invention, a filtercake offiller material is formed from at least a portion of the slurry that hasbeen process by a filter. The filtercake has a solid content of at leastabout 20 weight percent. In one non-limiting aspect of this embodiment,the solid content of the filtercake is about 25-75 weight percent. Inanother and/or alternative one non-limiting aspect of this embodiment,the solid content of the filtercake is about 30-50 weight percent. Instill another and/or alternative non-limiting embodiment of theinvention, liquid is removed from the filler material by use of one ormore dryers. Such drier can include, but are not limited to, tubularflash driers, ring flash drier, and the like. In one non-limiting aspectof this embodiment, the filler material is dried by the one or moredriers after the filler material has been processed by one or morefilters. As can be appreciated, the filler material is not required tobe filtered prior to being dried by one or more driers.

In another and/or alternative non-limiting aspect of the presentinvention, the filler material is collected in a bag or packagingprocess for final packaging. In one non-limiting embodiment of theinvention, the filler material can be screened prior to being bagged orpackaged so as to remove undesired sized particles of filler materialand/or contaminant. In another and/or alternative non-limitingembodiment of the invention, the filler material is bagged or packagedafter the filler material has been filtered and/or dried.

In still yet another and/or alternative non-limiting aspect of thepresent invention, the filler material of the present invention is usedas a component in paint. Such paints can include, but are not limitedto, water-based paints, solvent-based paints, etc. In one non-limitingexample, the filler material is included in a water-based paint. In onenon-limiting aspect of this example, the one or more polymers used inwater-based paints can include, but are not limited to, emulsionpolymers of vinyl acetate, styrene, styrene-butadiene, vinylacetate-vinyl chloride, acrylonitrile-butadiene, isoprene, vinylidenechloride-acrylonitrile, vinylidene chloride-vinyl acetate, vinylchloride-acrylonitrile, acrylic acid ester and methacrylic acid esterpolymers and copolymers thereof with other vinyl monomers, carboxylatedsynthetic and natural rubbers, and so forth. Other useful and well-knownwater-based paints include the epoxies, alkyds, phthalic alkyds,emulsified drying oils, polystyrene, and the like. In one specificnon-limiting example, the water-based paint is a latex paint. Onenon-limiting example of the latex paint can include vinyl acrylic latex;however, it can be appreciated that many other or additional types oflatex paints can be used.

It is one non-limiting object of the present invention to provide asilica coated metal fluoride compound and method of making such acompound.

It is another and/or alternative object of the present invention toprovide a silica coated metal fluoride compound from a waste steam thatincludes an acid that contains fluorine.

It is still another and/or alternative non-limiting object of thepresent invention to provide a silica coated metal fluoride compoundthat can be used as a filler and/or extender in various types ofproducts.

It is yet another and/or alternative non-limiting object of the presentinvention to provide a silica coated metal fluoride compound that can beused to improve the hiding power of a covering agent such as, but notlimited to, paint.

It is still yet another and/or alternative non-limiting object of thepresent invention to provide a silica coated metal fluoride compoundthat can be used to improve the matting properties of a covering agentsuch as, but not limited to, paint.

It is another and/or alternative non-limiting object of the presentinvention to provide a silica coated metal fluoride compound that can beused to impart chemical resistance to a covering agent such as, but notlimited to, paint.

These and other objects and advantages will become apparent to thoseskilled in the art upon the reading and following of this descriptiontaken together with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWING

Reference may now be made to the drawing, which illustrates onenon-limiting embodiment for manufacturing the filler material of thepresent invention;

FIG. 1 is a schematic view of a non-limiting process for producing afiller material by precipitation from a dilute aqueous solutioncontaining hydrofluorosilicic acid and hydrochloric acid.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to a material that can be used in avariety of applications such as, but not limited to, paint fillers. Thematerial can be used to improve the properties of a covering agent suchas paint. The material, when used as a pigment extender in a coveringagent, can be used as a partial or full substitute for previously usedcovering agent fillers such as, but not limited to, calcium carbonate.The material can be used to reduce the cost of the raw materials of thecovering agent without adversely affecting the properties of the paint.In some covering agent formulations, the material of the presentinvention can be used to increase the hiding power of the covering,reduce the sheen of the covering agent, improve the matting propertiesof the covering agent, improve the chemical resistence of the coveringagent, etc.

The material of the present invention is a metal fluoride compound thatis coated with silica. In one non-limiting embodiment of the invention,the material is a composite powder that includes silica-coated calciumfluoride crystal aggregates, amorphous silica particles, and discretecalcium fluoride crystals that are at least partially producedprecipitation from a dilute aqueous solution containinghydrofluorosilicic acid. The metal fluoride compound content of thematerial is about 55-80 weight percent of the material, and the silicacontent is about 10-35 weight percent of the novel material. The averageparticle size of the novel material of the present invention isgenerally no greater than about 100 microns. Typically, the averageparticle size of the novel material of the present invention isgenerally about 5-30 microns. As can be appreciated, larger or smallerparticle sizes can be used.

When the material is a silica-coated calcium fluoride crystal that isformed by the reaction between calcium fluoride and hydrofluorosilicicacid, the stoichiometry of the reaction is as follows:H₂SiF₆+3Ca(OH)₂═SiO₂+3CaF₂+4H₂O

The theoretical composition of the material according to the abovereaction is about 20.4 wt % SiO₂ and about 79.6 wt % CaF₂, based on acompletely dry product. The actual composition of the material producedby this reaction contains substantial quantities of structural waterpresent primarily in the amorphous silica. Loss on ignition of thematerial can vary from about 1-8 wt %. The hydrous silica phase losesits water gradually between 100° C. and 500° C. The bulk silica contentof the material can vary from about 15-30 wt %, while CaF₂, can varyfrom about 60-75 wt %. On non-limiting representative example of thematerial formed by the above reaction as identified by quantitativex-ray fluorescence spectrometry (XRF) is as follows: CaF₂ 72.1 SiO₂ 20.9Al₂O₃ 0.37 Ca(excess) 1.71 Cl 0.35 Fe₂O₃ 0.14 MgO 0.67 Na₂O 0.51 SO₃ 0.2LOI 3.1

All analyzed components in the above non-limiting example are in weightpercent. All the fluorine is assigned stoichiometrically to Ca, whichleft an excess of calcium. This excess calcium was assumed to be presentin solid solution with the amorphous silica. The LOI (loss on ignition)was measured at 600° C. The particle size analysis for the materialformed from the above reaction was determined by laser diffraction. Theparticle size distribution reveals a multi-modal distribution of theparticles of the material due to the various states of aggregation ofthe primary particles shown in the attached TEM photomicrographs. Theprimary crystallite size for the CaF₂ crystals was determined by themethod of x-ray diffraction line broadening as approximately, 50nanometers and is consistent with the TEM evidence. The measuredparticle size distribution of the material reflects the state ofaggregation of the primary particles, which are believed to be heldtogether, in part, by the amorphous silica gel. The mean particle sizefor the material was found to be between about 8-20 microns. Onenon-limiting particle size distribution is set forth below: Mean Size<10% <25% <50% <75% <90% <95% <99% 15.1 4.3 μm 6.0 μm 11.7 μm 22.1 μm32.4 μm 43.0 μm 52.0 μm μm

As can be appreciated, other particle size distributions can be formed.

As set forth above, the material of the present invention can be formedfrom precipitation from an aqueous solution containingfluorine-containing acid. As set forth in one non-limiting chemicalreaction above, the fluorine-containing acid can partially or fullyinclude hydrofluorosilicic acid. The fluorine-containing acid can alsoinclude another acid such as, but not limited to, hydrochloric acid;however, this is not required. A non-limiting method for forming thematerial is set forth as follows and is at least partially formed fromby precipitation from a dilute aqueous solution containinghydrofluorosilicic acid and hydrochloric acid. The precipitation isconducted in two-stages by the addition of hydrated lime into tworeactor vessels. The material formed by the process set forth in FIG. 1is a composite powder that contains silica-coated calcium fluoridecrystal aggregates, amorphous silica particles, and discrete calciumfluoride crystals that are produced by precipitation from a diluteaqueous solution containing hydrofluorosilicic acid. This non-limitingprocess for forming the filler material is illustrated in FIG. 1.

As illustrated in FIG. 1, the source of fluorine-containing acid istypically from a waste stream from another chemical process; however,this is not required. The concentration of the fluorine-containing acidin the waste stream is typically low. The concentration ofhydrofluorosilicic acid in supply stream 10 that is added to a steadystate tank 20 is typically about 0.5-1 weight percent. The pH of supplystream 10 is about 0.5-2, and typically about 1-2. The supply streamalso typically includes hydrochloric acid; however, this is notrequired. The pH in the steady state tank can be homogenized by stirringthe content of the tank; however, this is not required. The pH of thesteady state tank 20 can be moderated by recycling a portion of thecontents of the first reactor tank 50 back into the steady state tank 20via pipe 30. Fluid from the bottom portion of reactor tank 50 isdirected back to steady state tank 20; however, it can be appreciatedthat fluid from other or additional location in reactor tank 50 can bedirected into steady state tank 20. Typically one or more pumps are usedto cause fluid to flow from reactor tank 50 to steady state tank 20;however, this is not required. The solid content in the steady statetank is generally about 0-1 weight percent, typically about 0.1-0.6weight percent, and more typically about 0.2-0.4 weight percent. As canbe appreciated, some solids from reactor tank 50 may be introduced intosteady state tank 20 via pipe 30.

Pipe 40 directs fluid from a steady state tank 20 into the reactor tank.In the reactor tank, a source of base such as calcium oxide and/orcalcium hydroxide is added to the reactor tank 50 via supply tube 70from lime bin 60. The calcium oxide and/or calcium hydroxide typicallyhave an average particle size of less than about 50 microns; however,other particle sizes can be used. A sufficient amount of base is addedto reactor tank 50 cause the pH in the reactor tank to increase to about2-4 and typically about 2-3. A slurry is formed in reactor tank 50 whichcontains the silica-coated fluorspar particles that comprise the basisof this invention. The slurry in the reactor tank contains about 1-3weight percent solids. The contents in reactor tank 50 are typicallystirred to facilitate in the reaction; however, this is not required.

At least a portion of the slurry formed in reactor tank 50 is directedvia pipe 80 into a second reactor tank 90. Additional amounts of baseare added to reactor tank 90 via supply tube 100 from lime bin 60. Theslurry from reactor tank 50 is typically taken from the overflow fromreactor tank 50; however, it can be appreciated that the slurry can beat least partially taken from other or additional location in reactortank 50. A sufficient amount of base is added to the second reactor tank90 to cause the pH in the second reactor tank to increase to about 6-8pH. Reactor tank 90 is typically the location where the final pHadjustment for the slurry is obtained; however, this is not required.The solid content of the slurry in reactor tank 90 is generally about1-4 weight percent, and typically about 1-3 weight percent.

The slurry from reactor tank 90 is fed via pipe 110 into a slurrythickening tank 120. A flocculent agent is added to the slurry. Asillustrated in FIG. 1, a flocculent agent is added to pipe 110 via pipe140 from a flocculent agent source 130. As can be appreciated, theflocculent agent can be partially or directed added into slurrythickening tank 120. One or more polymers are typically used forflocculation of the slurry. One non-limiting example of a flocculentagent that can be used is Drewfloc 2270 manufactured by Ashland ChemicalCompany. The flocculent agent is typically added to the slurry from thereactor tank 90 a rate of about 0.05-0.15 weight percent based on thedry solid content of the slurry. The thickened slurry in slurrythickening tank 120 is allowed to settle in the slurry thickening tank.The solid content of the slurry that settles at or near the bottom ofthe slurry thickening tank is typically about 15-20 weight percent. Thedry solids in the slurry have an average specific surface area of about70-120 m²/g. Aging of solids can reduce the average specific surfacearea to about 35-60 m²/g.

The thickened slurry from the slurry thickening tank 120 is typicallyfed via tube 130 to a hydrocyclone 140; however, this is not required.The hydrocyclone is used to remove oversize particles and/orcontaminated particles in the thickened slurry via waste line 150.

After the slurry is processed in the hydrocyclone, the slurry is fed viapipe 160 to a de-watering unit such as a drum filter, cyclonic filter orthe like; however, this is not required. As illustrated in FIG. 1, adrum filter170 is used to at least partially remove liquid from theslurry to form a filtercake. The filtercake has a solid content of about30-50 weight percent.

The filtercake that is formed by the drum filter is dried such as by adrier such as a flash drying method, e.g., a tubular flash dryer or aring flash dryer 190; however, other or additional driers can be used.

Once the filtercake is dried, the material is collected in a bag orpackaged in a packaging process in bag house 200. The material can bescreened prior to being bagged or packaged so as to remove undesiredsized particles of material and/or contaminant; however, this is notrequired. The bagged or packaged material is a powder that containsprimarily silica-coated metal fluoride particles. The material is a finewhite powder having a Tappi brightness value of about 84-91. The averageparticle size of the material is generally up to about 100 μm, typicallyabout 3-60 μm, and more typically about 4-40 μm.

These and other modifications of the discussed embodiments, as well asother embodiments of the invention, will be obvious and suggested tothose skilled in the art from the disclosure herein, whereby it is to bedistinctly understood that the foregoing descriptive matter is to beinterpreted merely as illustrative of the present invention and not as alimitation thereof.

1. A material that includes a metal fluoride compound at least partiallycoated with a silicon compound.
 2. The material as defined in claim 1,wherein said metal fluoride includes calcium, M_(g,)N_(a).
 3. Thematerial as defined in claim 2, wherein said metal fluoride includescalcium fluoride.
 4. The material as defined in claim 1, wherein saidsilicon compound includes silicon dioxide.
 5. The material as defined inclaim 2, wherein said silicon compound includes silicon dioxide.
 6. Thematerial as defined in claim 3, wherein said silicon compound includessilicon dioxide.
 7. The material as defined in claim 1, wherein saidmetal fluoride compound constitutes about 50-99.9 weight percent of saidmaterial and said silicon compound constitutes about 0.1-50 weightpercent of said material.
 8. The material as defined in claim 6, whereinsaid metal fluoride compound constitutes about 50-99.9 weight percent ofsaid material and said silicon compound constitutes about 0.1-50 weightpercent of said material.
 9. The material as defined in claim 7, whereinsaid metal fluoride compound constitutes about 60-80 weight percent ofsaid material and said silicon compound constitutes about 20-40 weightpercent of said material.
 10. The material as defined in claim 8,wherein said metal fluoride compound constitutes about 65-75 weightpercent of-said material and said silicon compound constitutes about25-35 weight percent of said material.
 11. The material as defined inclaim 1, wherein said material is white and has a Tappi brightness valueof about 84-91.
 12. The material as defined in claim 8, wherein saidmaterial is white and has a Tappi brightness value of about 84-91. 13.The material as defined in claim 1, wherein said material has averagespecific surface area is less than about 120 m²/g.
 14. The material asdefined in claim 12, wherein said material has average specific surfacearea is less than about 120 m²/g.
 15. A method for forming a metalfluoride compound that is at least partially coated with a siliconcompound comprising: a) providing a source of an acid solution, saidacid solution including a fluorine-containing acid; b) providing a base;c) mixing said source of an acid solution and said source of base toform said metal fluoride compound that is at least partially coated witha silicon compound.
 16. The method as defined in claim 15, wherein saidsource of an acid solution at least partially from a waste stream. 17.The method as defined in claim 15, wherein said fluorine-containing acidincludes hydrofluorosilicic acid.
 18. The method as defined in claim 16,wherein said fluorine-containing acid includes hydrofluorosilicic acid.19. The method as defined in claim 15, wherein said source of an acidsolution has a pH of about 0.5-2.
 20. The method as defined in claim 15,wherein said base includes lime, hydrated lime, or mixtures thereof. 21.The method as defined in claim 15, including the step of adding saidsource of base to said source of an acid solution until a pH of themixture is at least about 5.5.
 22. The method as defined in claim 15,including the step of adding a flocculent agent to said formed metalfluoride compound that is at least partially coated with a siliconcompound.
 23. The method as defined in claim 15, including the step ofremoving oversize particles, contaminated particles, or combinationsthereof from said formed metal fluoride compound that is at leastpartially coated with a silicon compound.
 24. The method as defined inclaim 15, including the step of drying said formed metal fluoridecompound that is at least partially coated with a silicon compound. 25.The method as defined in claim 15, including the step of screening orclassifying said formed metal fluoride compound that is at leastpartially coated with a silicon compound so that an average particlesize is less than about 100 μm.